Table 1.

The main studies comparing the microbial communities of the small intestine and feces.

Subject	Sex	Sampling	Analysis Methods	Sampling Locations	Relationship	Year of Reported
Beagle dogs	M	Permanent jejunal fistula	Culture	Jejunum fluid, feces	Fecal samples were unable to represent the microbiota present in the upper gut.	2005 [32]
Human	M/F	Esophagogastro- duodenoscopy	16S rRNA gene sequencing	Stomach, duodenum, jejunum, feces	The small bowel microbiome was markedly different from that in the stool and varied between segments.	2020 [17]
Mongolian horses	M/F	Postmortem	16S rRNA gene sequencing	Stomach, foregut (jejunum, ileum), hindgut (cecum, colon)	The microbial community structures were significantly different among the stomach, foregut, and hindgut.	2020 [18]
Pig	M	Postmortem	16S rRNA gene sequencing	Whole gut	The fecal microbiome was insufficient to represent the whole gut microbiome.	2023 [34]
Human	M/F	Sampling capsule	16S rRNA gene sequencing	Small intestinal fluid, feces	Analysis of stool provided neither a complete nor an accurate representation of the longitudinal and temporal variability of the microbiota composition, virus activity, host proteome or bile acid contents within the intestines	2023 [35]
Beagle dogs	M/F	SIMBA™ capsule	16S rRNA gene sequencing	Small intestinal fluid, feces	A statistically significant difference in the microbial composition of capsules and feces was found.	2023 [36]

M/F: Male/Female; SIMBA™: small intestinal microbiome aspiration.